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Private database link
This link is more secure than a public or global link, because only the owner of the private link, or subprograms within the same schema, can use the link to access the remote database.

Public database link
When many users require an access path to a remote Oracle database, you can create a single public database link for all users in a database.

Global database link
When an Oracle network uses Oracle Names, an administrator can conveniently manage global database links for all databases in the system. Database link management is centralized and simple.

Users of Database Links
When creating the link, you determine which user should connect to the remote database to access the data. The following table explains the differences among the categories of users involved in database links:

User Type Meaning And Sample Link Creation Syntax

Connected user
A local user accessing a database link in which no fixed username and password have been specified. If SYSTEM accesses a public link in a query, then the connected user is SYSTEM, and Oracle connects to the SYSTEM schema in the remote database.

Note: A connected user does not have to be the user who created the link, but is any user who is accessing the link.

CREATE PUBLIC DATABASE LINK hq USING 'hq';

Current user
A global user in a CURRENT_USER database link. The global user must be authenticated by an X.509 certificate (an SSL-authenticated enterprise user) or a password (a password-authenticated enterprise user), and be a user on both databases involved in the link. Current user links are an aspect of the Oracle Advanced Security option.

CREATE PUBLIC DATABASE LINK hq CONNECT TO CURRENT_USER using 'hq';

Fixed user
A user whose username/password is part of the link definition. If a link includes a fixed user, then the fixed user's username and password are used to connect to the remote database.

CREATE PUBLIC DATABASE LINK hq CONNECT TO jane IDENTIFIED BY doe USING 'hq';

NK
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